The invention relates to a method for producing an integrated circuit, electronic device, or semiconductor device including a soldering connection. In such a method, two soldering partners are connected to one another by using a solder at an envisaged joining location.
Especially for the purpose of soldering electronic components, use is made of installations in which the components and the solder are heated in a chamber. The heating may be effected by using hotplates.
However, the heating of the soldering partners and the solder is effected by contact heat between the hotplate, on the one hand, and the soldering partners and the solder, on the other hand, and also by convection of the atmosphere situated in the chamber.
In order to achieve a specific temporal temperature profile at the material to be soldered, the material to be soldered, in the case of continuously heated hotplates, is supplied with energy in apportioned fashion by repeated docking and undocking of the material to be soldered at the hotplate. Since the hotplates have an increased temperature relative to the soldering temperature, in this way it is possible also to achieve steep temperature ramps at the material to be soldered.
This results in very great temperature jumps momentarily at the material to be soldered, which is reflected in a staircase- or sawtooth-like profile of the temperature at the material to be soldered.
If there is a large difference between the temperature of the hotplate and the temperature of the soldering partners, there is therefore the risk of thermal overshoot at the peak of the temperature profile, whereby they may be heated to an excessively great extent and be destroyed in the extreme case. In order to avoid this disadvantage, a relatively complicated docking and undocking mechanism is required.
A further disadvantage of this method consists in the fact that there is an increased energy consumption as a result of the continuous high level of heating of the hotplates.
In both methods, e.g., during the soldering of populated ceramic substrates onto precurved baseplates for power semiconductor modules, gas convection may be required for heating of the baseplates since, on account of the curvature, there is only poor direct thermal contact between baseplate and hotplate.
Soldering in a gas atmosphere has the disadvantage, however, that gas inclusions in the solder, that is to say the formation of voids, can occur. The volumes of the gas inclusions increase on account of further heating. This can give rise to spraying and to uncontrolled deposits of solder at component parts situated adjacent to the joining location.
Although the formation of voids could be avoided by soldering in a vacuum, in that case gas would no longer be available for convective heat transfer from the hotplate to the baseplate. The baseplate would be heated only via its contact locations with the hotplate, which, however, would result in a greatly nonuniform temperature distribution in the baseplate and hence highly inhomogeneous and qualitatively unsatisfactory soldering connection.
In addition, such a method would be associated with very long heating times since the heat transfer can only take place at the contact locations between the baseplate and the hotplate. Consequently, only very shallow temperature ramps could be produced at the baseplate.
The problem area outlined exists, of course, not only when soldering curved baseplates, but generally when soldering material to be soldered having an uneven surface.